1. Field of the Invention
The present invention is in the field of plant nutrition.
2. The Prior Art
It is well known that for optimizing plant growth it is desirable that the plant be supplied with nutriment at an essentially constant rate, e.g. that the concentration of nutrient to which the root structure of the plant is exposed be maintained at an essentially constant predetermined level or range.
Typically, in accordance with present practice, nutriments, such as fertilizer, mineral trace elements, etc., are administered intermittently, e.g. by occasional applications of fertilizer. As a result, the plant is exposed to high concentrations of nutriments directly after feeding, a procedure which may be dangerous to the plant and which is wasteful of the nutriment. For example, fertilizer in unduly high concentrations may burn the roots or may promote growth at an unduly rapid and, hence, unhealthy rate. Also, where the concentration of nutriment is so high that the plant is unable to assimilate it, increments of the nutriment will, in time, be leached from the soil to a position at which they can be of no benefit to the plant.
Typically, the high initial nutriment concentrations following application of fertilizer are followed by periods in which the concentration of fertilizer is undesirably low, with the result that the nutriment level is unpredictable.
It is feasible to water plants with a solution of fertilizer in desired concentration and thus maintain the fertilizer level in the growing medium at a desired concentration. However, such practice obviously requires the continuous reformulation of the water-nutrient solution, a procedure which is time-consuming and, to a degree, wasteful in that increments of the solution will pass clear of the root area of the plant. Additionally, there is a reluctance on the part of the user to handle or work with fertilizer products.
Numerous systems for maintaining fertilizer levels in a desired range without resorting to repeated applications have been attempted. By way of example, fertilizers or like nutriments have been combined with materials which are slow to dissolve whereby increments of the soluble components are released at each watering. While such procedure does, to a degree, reduce the amount of fertilizer immediately released upon watering and extend the period over which increments of fertilizer are released, the distribution of nutriment is nonetheless largely cyclical since each successive watering will release a reduced amount of nutriment.
Attempts have been made to saturate solid, porous, non-soluble masses with a nutriment in concentrated form, with the thought that, upon watering, quantities of nutriment will be extracted. Such procedure has proven unworkable for the desired purpose for several reasons. It has been found, for instance, that initial wettings preferentially extract nutriment from the external layers of the inert material, with the result that less and less soluble matter is extracted on subsequent wettings.
Additionally, soluble material tends to crystalize and clog the interstices within the initially porous mass, whereby subsequent wettings are prevented from entering into and extracting the material from the interior of the mass.
Still other procedures intended to maintain a constant nutriment level have resorted to a permeable waxy material encapsulating increments of nutriment.
Numerous drawbacks inhere in such products, and particularly a progressive reduction in fertilizer release with the passage of time. Additionally, in order to be effective, the pellets of waxy material are preferably disposed below the level of the soil and there is thus no way to determine when the fertilizer content has been effectively exhausted or, after exhaustion, to remove the inert and usually non-degradable materials from the soil.
To summarize, the use of so-called long acting nutriment systems heretofore known have failed to provide a means for accurately controlling nutriment concentrations in the soil over an extended time period.